The present invention relates to a digital mobile communication system such as a cellular system and so forth.
Conventionally, in a mobile communication system, when a radio area is intended to be enlarged, for instance, in a cellular system, when a radius of a cell is intended to be enlarged, the mobile communication system causes a transmission signal to be propagated in the distance while employing an amplifier with large amplification factor, since when a high-frequency wave is employed, a propagation loss is remarkable. In another way, enlargement of a radio area is performed in such a way that a mobile communication system places many base stations.
However, in a conventional mobile communication system, when an amplifier with large amplification factor is employed, it is necessary that the amplifier increases its amplification factor with progression of transmission in the distance. As a result, the size of an amplifier becomes considerably large. Thus there is a problem that the size of a base station becomes large in proportion to the size of an amplifier.
Moreover, there is a problem that power consumption of a mobile station apparatus becomes large because power required in a mobile station becomes large and also interference between adjacent cells is easy to occur with progression of size of the cell.
Furthermore, when many base stations are placed, there are problems that to secure installation places for base stations is difficult and/or an installed cost becomes high as a whole system. In this case, it is necessary for the mobile station to perform hand-over frequently, accordingly, it is difficult for the mobile station to perform communication during a high speed movement.
The present invention is achieved by taking account of this point. An object of the present invention is to provide a repeater apparatus capable of enlarging an radio area of a base station while suppressing an increase of the size of a base station, power consumption of a mobile station, the costs of the whole system, and interference in an adjacent cell.
This object is achieved in such a way that a repeater which is provided with a filter causing a specified channel to be passed is placed within a cell of a base station, and which passes specified frequencies used in the base station through the repeater and propagates them outer side of the cell in the distance. For this reason, it is possible to enlarge a cell area for only specified channel (specific frequency).